1. Technical Field of the Invention
The present invention relates to a method for providing cell location service in digital cellular mobile communication network, more particularly relates to a method for informing a cell location center of current location of a mobile station in which a base station identification is used for providing current location of the mobile station.
2. Description of the Prior Art
Many of concepts will be described below for helping to understand the preferred embodiment of the present invention.
Cell Location Service (CLS) is a service which informs the cell location center of current location of the mobile station. The cell location service may be implemented using different identifications communicated between the mobile station and the base station. Using the cell location service, vehicle location service or emergency location service may be easily implemented.
Short Message Service (SMS) is a service for transferring a short message between the mobile stations or between the mobile station and a message input terminal. The short message service is implemented by a short message service center (SMSC) which has a store and forward function.
Cell Location Center (CLC), which consists of computers, collects and processes location data of the mobile stations from the mobile communication network and provides external hosts with the location data.
Short Message Service Center (SMSC) is an apparatus which consists of computers and processes short message service, stores and forwards short messages.
Mobile Station (MS) has a function to process the cell location service. The mobile station may also process speech information.
The most prevalent location technology is the Global Positioning System (GPS). Obtaining a location fix is made possible by a timing and distance measurement, called triangulation, between a user on the earth's surface and a minimum of three of the 24 GPS satellites in orbit. GPS products are widely used in many commercial areas with mobile communication systems like cellular, personal communication systems (PCS) and paging. But GPS is unlikely to become the economic location technology because of requiring additional hardware to existing handset.
For locating mobile stations with no additional hardware, there are three basic technologies available: measuring signal attenuation, angle of arrival, or time difference of arrival(TDOA).
Most mobile station antennae are omni-directional, so power is dissipated rapidly in all directions. If the transmitted power of mobile station were known, and the power were measured at another point, distance could be estimated using one of several propagation models. But signals attenuate for reasons other than distance traveled, such as passing through walls, foliage, or glass and metal and other environmental factor.
The most common version of angle of arrival is known as small aperture direction finding, which requires a complex antenna array at each of several base stations. When several base stations can each determine their respective angle of arrival, mobile station location can be estimated from the point of intersection of projected lines drawn out from the base station at the angle from the signal originated. Small aperture angle of arrival systems suffer from distortion of the wavefront of the mobile station, caused by multipath and other environmental factors.
TDOA systems operate by placing location receivers at multiple sites geographically dispersed in a wide area; each of the sites has an accurate timing source. When a signal is transmitted from a mobile station, the signal propagates to all of the antenna sites where the signal reception is time stamped. The difference in stamps are then combined to produce intersecting hyperbolic lines from which the location is estimated. TDOA systems are also subject to many of the same urban multipath problems as angle of arrival systems.